Electric pressure-reducing valve

ABSTRACT

An electric pressure-reducing valve is provided for regulating a hydraulic utilization pressure by means of a low electric control current and comprises two stages, i.e., a primary stage constituted by a magnetic force motor and a stop-valve and jetnozzle system, and a secondary stage constituted by a hydraulic slide valve servo-controlled by the pressure regulated in the primary stage. The primary stage is wholly constructed along a single axis of revolution: the power developed by the magnetic force motor is directed along this axis, the movement of the stop-valve is a movement of translation along this axis, the jetnozzle is mounted on this axis; the primary stage is mounted on the body of the electric pressure-reducing valve so as to form an independent unit which is readily removable along said axis without any risk of upsetting the adjustments.

United States Patent [72] Inventor Rene Lucien Neuilly-sur-seine, France[21 App]. No. 800,323 [22] Filed Jan. 15, 1969 [45] Patented Aug. 17,1971 [73] Assignee Societe Anonyme elite: Messier Paris, France [32]Priority Jan. 15, 1968, Dec. 23, 1968 [33] France [31 l I 135,940 and179,987

[54] ELECTRIC PRESSURE-REDUCING VALVE,

6 Claims, 12 Drawing Figs.

[52] US. Cl l37/625.61, v 251/65 [51] Int. Cl...'. ..Fl6k 11/07,

[50] Field of Search ..l37/625.61,

[56] References Cited UNITED STATES PATENTS 2,625,136 1/1953 Moog137/6256] 2,790,427 4/1957 Carson 137/625.61 3,401,711 9/1968 Kubilosl37/625'.61 X 3,410,308 11/1968 Moog et al. 137/625.61 3,430,656 3/1969Hawk 137/625.6l 3,457,956 7/1969 Andrews 137/625.61

Primary Examiner-Henry T. Klinksiek AnorneyWaters, Roditi, Schwartz &Nissen ABSTRACT: An electric pressure-reducing valve is provided forregulating a hydraulic utilization pressure by means of a low electriccontrol current and comprises two stages, i.e., a primary stageconstituted by a magnetic force motor and a stop-valve and jet-nozzlesystem, and a secondary stage constituted by a hydraulic slide valveservo-controlled by the pressure regulated in the primary stage. Theprimary stage is wholly constructed along a single axis of revolution:the power developed by the magnetic force motor is directed along thisaxis, the movement of the stop-valve is a movement of translation alongthis axis, the jet-nozzle is mounted on this axis; the

primary stage is mounted on the body of the electric pressurereducingvalve so as to form an independent unit which is readily removable alongsaid axis without any risk of upsetting the adjustments.

ELECTRIC PRESSURE-REDUCING VALVE The present invention has for itsobject an apparatus known as an electric pressure-reducing valve, thefunction of which is to permit the control of a hydraulic pressure bymeans of a small electric control current.

For the same purpose, it is generally known to utilize servodistributors. This kind of apparatus usually gives satisfactory results,but it has the disadvantage of a high production cost.

The electric pressure-reducing valve according to the invention presentsthe advantage of having a much simpler construction and, consequently,being substantially less costly than its predecessors.

The electric pressure-reducing valve according to the inventioncomprises two stages, a primary stage constituted by a magnetic forcemotor and by a stop-valve and nozzle system, and a secondary stageconstituted by a hydraulic slide valve servo controlled by the pressureregulated by the primary stage.

The electric pressure-reducing valve in accordance with the invention isespecially characterized in that:

a. The primary stage'is wholly constructed along an axis of revolution:the power developed by the force-motor isdirected along this axis, themovement of the stop-valve is a translation along this axis, the nozzleor jet is placed on this axis; the primary stage is mounted on the bodyof the electric pressure reducing valve as an independent unit which isreadily removable by dismantling along the said axis, without risk ofinterfering with the adjustment; 7

b. For a constant supply pressure, and in the absence of hydraulic flow,the law of operation which associates the output pressure of theelectric pressure-reducing valve with its control current issubstantially linear;

c. in addition, if desired but not necessarily, the slope of the saidlaw of operation is independent of the supply pressure; in other words,the same variation of intensity of the control current always producesthe same variation of the utilization pressure, and these variations areproportional, over the range between the maximum supply pressure andzero pressure, which are physical limits of the utilization pressure.

In a more detailed manner, the law specified in (b) will be defined byreferring to the curves shown in FIG. 1, given by way of nonlimitativeexample, in which the intensity I of the electric control current isplotted on the abscissa and the utilization pressure PU delivered by thesecondary stage is plotted on the ordinate. With the electricpressure-reducing valve according to the invention, the law ofcurrent-pressure is linear (the straight line L in FIG. 1) for the valueof the supply pressure PAO at which the primary stage has been adjusted.On the other hand, when the supply pressure falls to a value PAl, lessthan PAO, the law of current-pressure has a level portion (the brokenline Ll of FIG. 1). The utilization pressure PU first remainssubstantially constant and equal to PAl as long as the control currenthas not reached a value IS, which value increases as the supply pressurePAl becomes lower.

' This characteristic with a flat-topped portion is obviously nottroublesome in applications in which the supply pressure PA isapproximately constant, and it still remains permissible in otherapplications. However, there exist applications in which the'supplypressure'is variable and in which furthermore. the said flat portion mayrepresent a disadvantage.

The invention enables this disadvantage to be eliminated when sodesired. According to a further arrangement of the invention, theelectric pressure-reducing valve can, according to paragraph (c) above,provide a law of current-pressure which With other arrangement accordingto the invention, for difierent values of PA, for example PAl, PA2, PA3,there is obtained a system of parallel straight lines,- allcharacterized by a constant ratio between the variation of .the controlcurrent intensity I and the variation of the utilization pressure PU. Itwill be observed that the level pressure zones suchas that shown in FIG.1 have been eliminated.

Briefly, following an arrangement in accordance with the invention, inthe electric pressure-reducing valve comprising a primary stage and asecondary stage, the primary stage comprising a magnetic force motor, amoving stop-valve displaced by the said motor, a noule placed in frontof the said stopvalve, and an orifice plate mounted upstream of the saidnozzle and supplied under pressure by a hydraulic source, the secondarystage comprising a hydraulic slide valve controlled by the controlpressure established by the primary stage betweenthe said orifice plateand the said nozzle and regulating the said utilization pressure, withzero hydraulic flow, following a law as a function of the electriccontrol current which is substantially linear for a constant supplypressure, the said primary stage is wholly constructed along an axis ofrevolution Y-Y, the power developed by the said force-motor beingdirected along the said axis Y-Y, the movement of the said stop-valve isin translation along the said axis Y-Y, thesaid nozzle is a body ofrevolution about the said axis Y-Y, the whole of the primary stage beingcapable of removal as a unit along the said axis Y-Y, and the saidhydraulic slide valve is acted upon in opposite directions, overtwo'equal sections, on the one hand by the said control pressure and onthe other hand by the said utilization pressure, the said hydraulicslide valve having a neutral position in which it does not modify thesaid utilization pressure, on one side of which it is displaced if theutilization pressure becomes less than the prescribed value and in whichit connects the said utilization pressure to exhaust.

Briefly, following another arrangement according to the invention, inthe electric pressure-reducing valve comprising a primary stage and asecondary stage, the primary stage comprising a magnetic force-motor, amovable stop-valve displaced by the said motor, a nozzle placed in frontof the said stop-valve, and an orifice plate mounted upstream of thesaid nozzle and supplied under pressure by a hydraulic source, thesecondary stage comprising a hydraulic slide valve controlled by thecontrol pressure established by the primary stage is always linear andof constant slope, in spite of variations of supply pressure. This lawaccording to (c) will be defined by referring to the curves given inFIG. 2 by way of nonlimitative example, these curves also having theintensity I of the electric control current plotted on the abscissa andthe utilization pressure PU on the ordinate.

between the said orifice plate and the said nozzle and regulating thesaid utilization pressure, at zero hydraulic flow, following a law as afunction of the electric control current which is substantially linearfor a constant supply pressure and has a substantially constant slopefor a variable supply pressure, the said primary stage is whollyconstructed along an axis of revolution Y-Y, the power developed by thesaid force-motor is directed along the said axis Y-Y, the movement ofthe said stop-valve is in translation along the said axis Y-Y, the saidnozzle is a body of revolution about the said axis Y-Y, the whole of theprimary motor can be removed as a unit along the said axis Y-Y, and thesaid hydraulic slide valve is acted upon in opposite directions, on theone hand over a first section by the said control pressure and over asecond section by the said utilization pressure, and on the other handover a third section equal to the said second section by the said supplypressure, the said hydraulic slide valve having a neutral position inwhich it does not modify the said utilization pressure, on one side ofwhich it is displaced if the utilization pressure becomes less than theprescribed value and at which it supplies the said utilization pressurefrom the said supply pressure, and on the other side of which it isdisplaced if the utilization pressure becomes greater than theprescribed value and at which it connects the said utilization pressureto exhaust.

The invention, and two embodiments of the electric pressure-reducingvalve according to the invention, will now be described with referenceto the accompanying drawings, given by way of nonlimitative examples. Inthese drawings:

FIG. 3 is a diagrammatic view in axial section of an electricpressure-reducing valve according to the invention, providing the law ofcurrent-pressure shown in FIG. 1;

. FIG. 4 is the view in elevation corresponding to FIG. 3;

FIG. 5 is a view inaxial section taken along the line V-V of FIG. 4, butto twice the scale;

FIG. 6 is a view in cross section taken along the line- VI-VI of FIG. 5;

FIG. 7 is a view in cross section along the line VII-VII of FIG. 4;

FIG. 8 is a view in plan looking from above, of FIG. 4;

.FIGv 9 is a view in half-longitudinal section of the secondary stage; I

FIG. 10 shows a further electric pressure-reducing valve according tothe invention, in cross section passing through the axis X-X of theslide valve of the secondary stage and normal to the axis Y-Y of theprimary stage;

FIG. 11 is a cross section passing through the axis Y-Y of the primarystage and normal to the axis X-X of the slide valve of the secondarystage, taken along the line XIV-XI of FIG. 10;

FIG. 12 is a detail, in cross section through the axis Y-Y of theprimary stage, along the line XII-XII of FIG. 10, showing the electricalconnections of the operating coil.

' With reference to FIGS. 3 and 5,'there will be described below thestructure of the primary stage of this electric pressure-reducing valveaccording to the invention.

The magnetic motor, of the polarized type, comprises a permanent magnet1 with radial magnetization, a coil 2, a moving core 3 and a magneticcircuit consisting of the parts 4, 5 and 6. The airgap 7 is determinedby the space comprised between the core 3 and thepart 4. The airgap 8corresponds to the space comprised between the said core 3 and the part5, and the airgap 9 to the space comprised between the said core 3 andthe part 6. The core 3 is rigidly fixed to a rod 1 1, the twoextremities of which are respectively suspended from two fine metallicdiaphragms l2 and 13. The core 3 can thus move without frictionalcontact on any other member. Two springs 14 and 15 ensure its return toits mean position. The support 6 on which the spring 14 is indirectlysupported, comprises a screw 17 which, by acting on the cup 18 of thisspring enables the position of the core 3 to be adjusted.

Magnetic shunts 19 arranged in holes formed in a spacing member 21 ofthe magnetic circuit 4 permit the adjustment of the gainof theforce-current law. A closure member or stop valve 23, fixed to theextremity of the rod 11 opposite to the screw 17 is mounted facing ajet-nozzle 24 with lateral outlets 25a, the. whole being arranged, asalready stated, along the general axis Y-Y. This primary stage finallycomprises an orifice plate 25 protected by a filter 26.

All the elements of this primary stage are contained in a body 27 andthus constitute an independent unit, which can be extracted from theremainder of the apparatus without risk of putting it out of adjustment.This body 27 is extended by an endpiece 28 fixed on the body 27 by a nut29 (see FIG. 5). This endpiece l8 is-in turn closed by the base of thefluidtight electric socket 30.

The secondary stage-having an axis X-X (see FIGS. 3, 7, 8 and 9),comprises a slide valve 31 moving inside a casing 32 and acted upon bytwo restoring springs 34 and 35. The chamber 36 (FIGS. 3 and 9), locatedat one of the extremities of the slide valve, communicates continuouslywith the chamber 37 comprised between the nozzle jet 24 and the orificeplate 25 (FIGS. 3 and 5), in which the primary stage regulates thecontrol pressure PC. At the opposite extremity of the slide valve 31,the chamber 38 communicates with the utilization orifice (pressure PU).Theelements of this secondary stage are mounted in a body 39 on whichthe primary stage is fixed in a removable manner.

The casing 32 is held in position by the endpiece4l, which comprises ascrew 42 by means of which the law of currentpressure can be adjusted.An endpiece 43 closes the chamber 36. Finally, on the body 39 areprovided the three hydraulic connections for supply (pressure PA),utilization (pressure PU) and return R (FIGS. 3, 4, 7 and 8), togetherwith the fixing lugs (not shown).

The operation of this electric pressure-reducing valve is effected asfollows:

According to the shape of the current-pressure characteristic vwhich itis desired to obtain, the utilization pressure PU is a substantiallylinear function, increasing or decreasing, of the current I passingthrough the coil 2, on the assumption that the supply pressure PA isconstant.

There is considered for example the case in which the pressure PU is adecreasing function of I. When the current I is zero, the stop-valve orclosure member 23 occupies a position very close to the jet nozzle 24,at a distance which can be adjusted by means of the screw 17 in order toobtain the desired maximum pressure of PU. In fact, this distancedetermines the pressure in the chamber 37. As long as the pressure PU isless than the pressure PC existing at 37, the slide valve 31 movestowards the left (FIG. 5) and it delivers from PA towards PU. Inconsequence, the pressure PU progressively increases; the slide valve 31closes its passages when an equilibrium of the pressures is reached.

When the current I is not zero, the magnetic motor applies to the movingcore 3 a force which, acting in opposition to that applied by thesprings 14 and 15, moves the closure member 23 away from the jet nozzle24, which has the effect of reducing the pressure in the chamber 37. Theresult is that the slide valve 31 is displaced towards the right andputs the utilization PU incommunication with the return R, up to themoment when an equilibrium of the pressures is again obtained, but at alower value.

It is clear that the force applied on the core by the magnetic motor hasfor its origin the combination in the airgaps 7 and 9, 1

of the flux generated by the coil 2, with the flux created by thepermanent magnet of the groove 64 of the casing, a groove 74 which cancome opposite passages 64 of the latter flux being distributed betweenthe airgaps 7 and 9, after having passed across the airgap 8. I 7

It will be understood that the particular constructional features of theelectric pressure-reducing valve described above are not of anylimitative nature.

Another electric pressure-reducing valve according to the invention,which ensures the current-pressure law shown in FIG. 2, will now bedescribed with reference to FIGS. 10 to 12.

Referring to FIG. 10, the secondary stage of this embodiment comprises,housed in a body 51 in a fluidtight manner, as

shown, a cylindrical casing 52 having an axis X-X mounted between twosockets 53 and 54 forming abutments and two fluidtight plugs 55 and 56held by threaded nuts 57 and 58 screwed on the body 51. A cylindricalslide valve 59 having an axis X-X slides freely between thesocket-abutments 53 and 54.

The casing 52 is provided with a plurality of external grooves, eachcommunicating with radial passages, namely, going from left to right inFIG. 10: a groove 61 which is connected (in a manner not shown), to thereturn to the tank and therefore under pressure; a groove 62 connectedto the utilization conduit and therefore under the utilization pressurePU; a groove 63 coupled to the supply conduit and therefore under thesupply pressure PA; a groove 64 which is also under the utilizationpressure PU; and a groove 65 connected to the output of the primarystage and therefore under the control pressure PC.

The slide valve 59 is provided externally with a plurality of externalgrooves, separated from each other by three shoulders, namely, goingfrom left to right in FIG. 10: an endpiece 71 of reduced diameter, agroove 72 which can come opposite passages of the groove 61 of thecasing and which faces passages of the groove 62 of the casing, a groove73 which is facing the groove 63 of the casing and which can comeopposite passages 64 of the casing, and an endpiece 75 of reduceddiameter.

An axial and then radial passage 76 provides a continuous communicationbetween the chamber 77 on the left-hand side of the slide valve and thegroove 73, and a radial then axial passage 78 forms a continuouscommunication between the groove 74 and the chamber 79 on the right-handside of the slide valve.

To sum-up, to the left of a central position, the slide valve puts itsgroove 72 into communication with the grooves 61 and 62 of the casing 52and thus connects the utilization conduit to the return to the tank,which reduces the utilization pressure PU, and to the right of thiscentral position, the groove 73 of the slide valve 59 puts intocommunication the grooves 63 and 64 of the casing 52, and therefore putsthe supply conduit into communication with the utilization conduit,which increases the utilization pressure PU.

Now, the slide valve 59 slides freely in the casing 62 under the actionof the hydraulic pressureswhich are applied to it, and which are: on theone hand in the left-hand chamber 77, the supply pressure PA arrivingthrough the groove 63, the groove 73 and the axial passage 76,, andacting towards the right on the annular section S1 of the endpiece 71,on the other hand, in the right-hand chamber 79, the utilizationpressure PU coming in through the groove 64,, the groove 74 and theaxial passage 78, and acting towards the left on the annular section ofthe endpiece 75, which has the same annular section S1 .as the endpiece71, and finally the control pressure PC, coming in through the groove 65and acting towards the left on the annular section In consequence, theslide valve 59 will be in equilibrium if: v

(PA)( )HP X Z) therefore:

With reference to FIG. '11 the magnetic motor of the polarized typecomprises a permanent magnet 81 with radial magnetization, a coil 82 amoving core 83 and a magnetic circuit composed of the members 84, as and86. The working airgaps 8 7 and 8,8 correspond respectively to the spacecomprised between the core 83 and the member 84, nd to the spacecomprised between the said core and the member 86. The core 83 isrigidly fixed to a rod 89, the two extremities of which are suspendedrespectively from, two thin metallic diaphragms 91 and 9,2; the core 83is thus able to move without rubbing contact with any other part. Theelastic, return'of the moving system 83-89, is ensured by the twodiaphragms 91. and 92 which are notched; and tend to lift this movingsystem, and by a. helicoidal spring 93 which tends to pull it down. Thisspring 9,3 works in compression and its supporting point 94,. can bedisplaced by an adjustment-screw 95, c i th ughv a th aded p ug 9 Theabove members ofthe primary stage are housed in a cylindrical chimney97, having an axis, Y.Y, of the body 51,, lo e y an endpla e 98- nd anut 9 The two connection wires 10,1, of the coil 82 (see FIG. 12.) passintov a recess formed" in the, body 51 and; are connected to aneleqtrijcsocket 103 which is, removable by means of screws 1',04'.(Se 8FIG. 1-0.).

in the body 511 and again along the axis Y-Y is formed a chamber; 111,in, which a closure member 112', fixed to the lower extremity of therod} 89 and therefore movable in translation parallel} to the axis Y-.Y,moves in front of'a jetnozzle 1'13, mountedin a. fixed: position alongthe, axis Y-Y and. withfluidtight sealing in the body- 51. This jetnozzle, 1.1'3 is-v fed through the intermediary ofan orifice plate; 114and a cylindrical filter 1 from the supply conduit 116. The jet nozzle1'13. and its, associated parts. are held by. a plug 1 1'7 and; a screw11,8.and. are thus e sily c ssible- When the actionv of the magneticmotorbrings the,- closure member 1121- clo er: to he. j male 113, the;pressure in the chamber 119: upstream of'the jet nozzle increases. Thispres sure is the control; pressure PC and is. sent via lateral openings113g in nozzle; 1;1 3.into,the groove, 65 of the secondary. stagethrough a-conduit-system (not shown).

It will be noted that, with the arrangements described above, on the onehand the hydraulic portion of the primary stage is readily accessible,for example in order to clean the filter or the jet nozzle, and on theother hand, its electrical portion is easily accessible. In addition,these parts are interchangeable by means of the adjustment alone of thespring 93 by its screw 95. These advantages are obviously associatedwith the systematically axial structure (with an axis Y-Y) given to thetwo hydraulic and electrical portions of the primary stage of theelectrodistributor.

On the other hand, the direction of the current I in its coil 82 is suchthat it produces a control pressure PC at the output of the primarystage which is an increasing function of the current:

3. (PC)=kl in which k is a positive constant. A combination of theequations (2) and (3) shows that:

4. (PU)=(PA)-al 1 in which a is a constant equal to (S2/S1)-k. In otherwords, the slope a of the straight line representing thecurrent-pressure law is independent of the supply pressurePA. This iswhat is shown in FIG. 2.

From the technological point of view, the construction of the secondstage shown in FIG. 10 should be noted. The two endpieces 71 and aremachined on the slide valve 59 in a concentric manner with respect tothe three bearing surfaces which slide in the bore of the casing. Thetwo sockets 53 and 54 are centered in the bore of the casing 52, thesesockets each comprising a bore in which is allowed to slide one of theendpieces 71 and 75. It can thus be seen that as a result of thecentering of the sockets 53 and 54 in the casing 52, there are only twoconcentricities to be observed: that of the end pieces 71 and 75 withthe three bearing surfaces of the slide valve, and that of the bore andthe external machining of the sockets 53 and 54. These twoconcentricities can furthermore be obtained with a high degree ofaccuracy by a single machining operation. In fact, by means of anappropriate jig, the sockets 5.3 and 54 can be held on the endpieces 71and 75, and in a single operation it is possible to grind the threebearing surfaces of the slide valve and the external diameters of thesockets 53: and 54.

In this way it is possible to obtain almost perfect concentricities andin consequence to provide a frictionless sliding movement of the slidevalve, at the same time having very small clearances (between the slidevalve 59' and the casing 52, between the endpieces 71 and 75 and betweenthe sockets 53. and 54: and finally between the sockets 53 and 54 andthe casing). These small clearances enable very small friction to beobtained at the level, of the second stage.

In addition, it will be observed that the two passages 76 and 78in the.interior of the slide valve 59, which on the one hand bring the pressurePA into the chamber 77' and on the other hand lead the pressure PU intothe chamber 79 permit the machining-of the body 51 to be simplified.

What 1 claim is:

1'. An electric pressure-reducing valve for regulating a hydraulicutilization pressure as a function of a lowelectric control current,comprising a primary stage and a secondary Stage, the primary stagecomprising'a magnetic force motor, a movable, closure member coupledtoand displaced by said motor; a jet-nozzle. placed: in front of saidclosure member, and an orifice: plate mounted upstream of'said jetnozzle and supplied under pressure by' a hydraulic source, the secondarystage comprising a hydraulic slide valve controlled by thecontrolpressure established. by the: primary stage between: said orificeplate and said jet-nozzle and regulating said utilization pressure with.zerov hydraulicv flow as a. function of'the electric controbcurrentwhich is substantially; linear for a. constant supply pressure,said primary stage. being wholly. constructed. along an.- axis. ofrevolution Y-Y, the power devel'oped bysaidforce-motor being directedalongsaid; axis Y-Y', the movement of said; closure member by said motorbeingl transla-- tion. along said axis; Y'Y, said jet-nozzle. being abody ofrevolution about said axis Y-Y, means supporting the whole of theprimary stage as aremovable unit along said axis Y-Y, means forsupplying said hydraulic slide valve in opposite directions, on twoequal sections, on the one hand with said control pressure and on theother with said utilization pressure, and means providing said hydraulicslide valve with a neutral position in which it does not modify saidutilization pressure, on one side of which it is displaced if theutilization pressure becomes less than the prescribed valueand in whichit supplies said utilization pressure from said supply pressure, and onthe other side of which it is displaced if said utilization pressurebecomes higher than the prescribed value and in which it causes saidutilization pressure to escape.

2, An electric pressure-reducing valve as claimed in claim 1, in whichsaid motor of said primary stage comprises a permanent magnet with anaxis Y-Y, with radial magnetization, a coil on the axis Y-Y, a movablecore on the axis Y-Y, a magnetic circuit comprising two end plates, ayoke with its axis Y-Y with a spacing member and adjustable magneticshunt means in said spacing member, a rod with its axis Y-Y rigidlyfixed to said movable core, two thin metal diaphragms supporting saidrod, an adjustable spring with its axisY-Y at one extremity of said rod,said closure member with its axis Y-Y being at the other extremity ofsaid rod, said means supporting the primary stage asa removable unitcomprising a body on the axis YY housing all said members of the primarystage.

3. An electric pressure-reducing valve as claimed in claim 1 whereinsaid means providing the slide valve with its neutral position comprisesa casing slidably receiving said hydraulic slide valve therein, and twoopposing springs, one of which includes adjustable means, said springsacting on said slide valve for restoring said slide valve to its neutralposition, said means for supplying the hydraulic slide valve with theutilization and control pressures comprising at one extremity of saidcasing an endpiece closing a first chamber connected to and subjectedto-said utilization pressure, at the other extremity of said casing, anendpiece closing a second chamber connected to and subjected to saidcontrol pressure, said slide valve being provided with a blind axialbore and grooves positioned to cooperate with grooves in said casing forsupplying said utilization pressure from said supply pressure when theslide valve is displaced towards the first said chamber, and in causingsaid utilization pressure to escape when said slide valve is displacedtowards said second chamber.

4; An electric pressure-reducing valve for regulating a hydraulicutilization pressure as a function of a low electric control current,comprising a primary stage and a secondary stage, said primary stagecomprising a magnetic force motor, a movable closure membercoupled toand displaced by said motor, a jet-nozzle placed in front of saidclosure member, and an orifice plate mounted upstream of said jet-nozzleand supplied under pressure by a hydraulic source, said secondary stagecomprising a hydraulic slide valve controlled by the control pressureestablished by the primary stage between said orifice plate and saidjet-nozzle and regulating said utilization pressure, at zero hydraulicflow as a function of the electric control current which issubstantially linear for a constant supply pressure and substantially ofconstant slope for a variable supply pressure, said primary stage beingwholly constructed following an axis of revolution, the power developedby said force-motor being directed along said axis, the movement of saidclosure member by said motor being in translation along said axis, saidjet-nozzle being a body of revolution about said axis, means supportingthe whole of the primary motor as a removable unit along said axis,means for supplying said hydraulic slide valve in opposite directions,on the one hand on a first section by said control pressure and on asecond section by said utilization pressure and on the other hand on athird section equal to said second section bysaid supply pressure, andmeans providing said hydraulic slide valve with a neutral position inwhich it does not modify said utilization pressure, on one side of whichit is displaced if the utilization pressure becomes less than theprescribed value and in which it supplies saidutilization pressure fromsaid supply pressure, and on the other side of which it is displaced ifthe utilization pressure becomes greater than the value prescribed andin which it causes said utilization pressure to escape.

5. An electric pressure-reducing valve as claimed in claim 4, in whichsaid motor of said primary stage comprises a permanent magnet having anaxis Y-Y, with radial magnetization, a coil on the axis Y-Y, a movablecore on the axis Y-Y, and a magnetic circuit comprising two end platesand a yoke having the axis Y-Y, a rod on axis Y-Y rigidly fixed to saidcore, two thin metal diaphragms supporting said rod, an adjusta'blespring means on the axis Y-Y, at one extremity of said rod, said closuremember being on the axis Y-Y, at the other extremity of said rod, saidmeans supporting the primary stage as a removable unit comprising acylindrical chimney with the axis Y-Y housing all said members of theprimary stage.

6. An electric pressure-reducing valve as claimed in claim 4 furthercomprising a casing slidably receiving said hydraulic slide valve, saidmeans for supplying the hydraulic slide valve with the utilization andcontrol pressures comprising at one extremity of said casing asocket-abutment and a plug defining a first chamber having a determinedsection on which is applied said supply pressure, at the other extremityof said casing, a socket-abutment and a plug defining a second chamberhaving the same section as said first chamber, on which is applied saidutilization pressure, an intermediate shoulder of said slide valveforming therein an annular surface constituting said first section onwhich said control pressure is applied in the direction which pushes theslide valve towards said first chamber, said slide valve being providedwith two blind axial bores and with grooves positioned to cooperate withgrooves of said casing in supplying said utilization pressure from thesupply pressure when the slide valve is displaced towards said secondchamber and in causing said utilization pressure to escape with saidslide valve is displaced towards said first chamber.

1. An electric pressure-reducing valve for regulating a hydraulicutilization pressure as a function of a low electric control current,comprising a primary stage and a secondary stage, the primary stagecomprising a magnetic force motor, a movable closure member coupled toand displaced by said motor, a jet-nozzle placed in front of saidclosure member, and an orifice plate mounted upstream of said jet-nozzleand supplied under pressure by a hydraulic source, the secondary stagecomprising a hydraulic slide valve controlled by the control pressureestablished by the primary stage between said orifice plate and saidjet-nozzle and regulating said utilization pressure with zero hydraulicflow as a function of the electric control current which issubstantially linear for a constant supply pressure, said primary stagebeing wholly constructed along an axis of revolution Y-Y, the powerdeveloped by said force-motor being directed along said axis Y-Y, themovement of said closure member by said motor being in translation alongsaid axis Y-Y, said jetnozzle being a body of revolution about said axisY-Y, means supporting the whole of the primary stage as a removable unitalong said axis Y-Y, means for supplying said hydraulic slide valve inopposite directions, on two equal sections, on the one hand with saidcontrol pressure and on the other with said utilization pressure, andmeans providing said hydraulic slide valve with a neutral position inwhich it does not modify said utilization pressure, on one side of whichit is displaced if the utilization pressure becomes less than theprescribed value and in which it supplies said utilization pressure fromsaid supply pressure, and on the other side of which it is displaced ifsaid utilization pressure becomes higher than the prescribed value andin which it causes said utilization pressure to escape.
 2. An electricpressure-reducing valve as claimed in claim 1, in which said motor ofsaid primary stage comprises a permanent magnet with an axis Y-Y, withradial magnetization, a coil on the axis Y-Y, a movable core on the axisY-Y, a magnetic circuit comprising two end plates, a yoke with its axisY-Y with a spacing member and adjustable magnetic shunt means in saidspacing member, a rod with its axis Y-Y rigidly fixed to said movablecore, two thin metal diaphragms supporting said rod, an adjustablesprinG with its axis Y-Y at one extremity of said rod, said closuremember with its axis Y-Y being at the other extremity of said rod, saidmeans supporting the primary stage as a removable unit comprising a bodyon the axis Y-Y housing all said members of the primary stage.
 3. Anelectric pressure-reducing valve as claimed in claim 1 wherein saidmeans providing the slide valve with its neutral position comprises acasing slidably receiving said hydraulic slide valve therein, and twoopposing springs, one of which includes adjustable means, said springsacting on said slide valve for restoring said slide valve to its neutralposition, said means for supplying the hydraulic slide valve with theutilization and control pressures comprising at one extremity of saidcasing an endpiece closing a first chamber connected to and subjected tosaid utilization pressure, at the other extremity of said casing, anendpiece closing a second chamber connected to and subjected to saidcontrol pressure, said slide valve being provided with a blind axialbore and grooves positioned to cooperate with grooves in said casing forsupplying said utilization pressure from said supply pressure when theslide valve is displaced towards the first said chamber, and in causingsaid utilization pressure to escape when said slide valve is displacedtowards said second chamber.
 4. An electric pressure-reducing valve forregulating a hydraulic utilization pressure as a function of a lowelectric control current, comprising a primary stage and a secondarystage, said primary stage comprising a magnetic force motor, a movableclosure member coupled to and displaced by said motor, a jet-nozzleplaced in front of said closure member, and an orifice plate mountedupstream of said jet-nozzle and supplied under pressure by a hydraulicsource, said secondary stage comprising a hydraulic slide valvecontrolled by the control pressure established by the primary stagebetween said orifice plate and said jet-nozzle and regulating saidutilization pressure, at zero hydraulic flow as a function of theelectric control current which is substantially linear for a constantsupply pressure and substantially of constant slope for a variablesupply pressure, said primary stage being wholly constructed followingan axis of revolution, the power developed by said force-motor beingdirected along said axis, the movement of said closure member by saidmotor being in translation along said axis, said jet-nozzle being a bodyof revolution about said axis, means supporting the whole of the primarymotor as a removable unit along said axis, means for supplying saidhydraulic slide valve in opposite directions, on the one hand on a firstsection by said control pressure and on a second section by saidutilization pressure and on the other hand on a third section equal tosaid second section by said supply pressure, and means providing saidhydraulic slide valve with a neutral position in which it does notmodify said utilization pressure, on one side of which it is displacedif the utilization pressure becomes less than the prescribed value andin which it supplies said utilization pressure from said supplypressure, and on the other side of which it is displaced if theutilization pressure becomes greater than the value prescribed and inwhich it causes said utilization pressure to escape.
 5. An electricpressure-reducing valve as claimed in claim 4, in which said motor ofsaid primary stage comprises a permanent magnet having an axis Y-Y, withradial magnetization, a coil on the axis Y-Y, a movable core on the axisY-Y, and a magnetic circuit comprising two end plates and a yoke havingthe axis Y-Y, a rod on axis Y-Y rigidly fixed to said core, two thinmetal diaphragms supporting said rod, an adjustable spring means on theaxis Y-Y, at one extremity of said rod, said closure member being on theaxis Y-Y, at the other extremity of said rod, said means supporting theprimary stage as a rEmovable unit comprising a cylindrical chimney withthe axis Y-Y housing all said members of the primary stage.
 6. Anelectric pressure-reducing valve as claimed in claim 4 furthercomprising a casing slidably receiving said hydraulic slide valve, saidmeans for supplying the hydraulic slide valve with the utilization andcontrol pressures comprising at one extremity of said casing asocket-abutment and a plug defining a first chamber having a determinedsection on which is applied said supply pressure, at the other extremityof said casing, a socket-abutment and a plug defining a second chamberhaving the same section as said first chamber, on which is applied saidutilization pressure, an intermediate shoulder of said slide valveforming therein an annular surface constituting said first section onwhich said control pressure is applied in the direction which pushes theslide valve towards said first chamber, said slide valve being providedwith two blind axial bores and with grooves positioned to cooperate withgrooves of said casing in supplying said utilization pressure from thesupply pressure when the slide valve is displaced towards said secondchamber and in causing said utilization pressure to escape with saidslide valve is displaced towards said first chamber.